DNA Replication
What is DNA?


Stands for Deoxyribonucleic
Acid
Has three main parts:
1.
Sugar molecules
(deoxyribose)
2.
Phosphate
3.
Nitrogen bases
**the deoxyribose and the
phosphate make up the
backbone while the nitrogen
bases join the two
backbones in the middle
(looks like a ladder!)
The structure of DNA is called a
double helix, because of the
way in which the two
backbones wrap around
one another
What are nitrogen bases?

Four different
nitrogen bases exist
in DNA: adenine (A),
thymine (T),
Guanine (G) and
cytosine (C)
 Adenine always
pairs with thymine
and guanine always
pairs with cytosine
Why are nitrogen bases
important?
 The
sequence of nitrogen bases makes
up what we call GENES
 Each gene controls the production of a
protein
 This in turn controls all of the traits and
characteristics that make each of us an
individual
How is DNA duplicated?



Before cells divide, they
must duplicate their
genetic material
This process is called
DNA replication
The first step in this
process involves an
enzyme that “unzips”
the two strands in the
original DNA molecule
DNA replication (continued)

As the original DNA strand unzips, another
enzyme moves along each strand, attaching
complimentary nitrogen bases to replace
those that were separated
 When all of the new bases have been placed,
two new molecules of DNA have been
formed, each one identical to the original
strand
What happens when DNA is
not replicated properly?

We all make mistakes in our daily lives!
 Mistakes can also happen in DNA
replication
 Such mistakes are called MUTATIONS
 Mutations fall into one of three categories:
1.
2.
3.
POSITIVE – one that benefits the organism
NEUTRAL – one that has no effect on the
organism
NEGATIVE – one that is harmful to the organism